For some time there has existed a need for extended controlled ventilation in patients with severe lung ailments. In one procedure which has been devised to meet this need, endo-tracheal intubation has been devised which comprises inserting a tube through the upper airways (trachea) of the patient. The tube is then used to connect the respiratory apparatus of the patient to a mechanical ventilating device or respirator.
For a number of reasons it is usually necessary to form a seal between the endo-tracheal tube and the inside of the tracheal wall of the patient. The extended controlled ventilation requires intermittent pressurization of the patient's respiratory apparatus, and the seal is necessary if a pressure above atmospheric is to be maintained within the patient's respiratory system. To obtain this seal, the endo-tracheal tube is provided with a cuff which is capable of being inflated once in place. Since the patient may require the use of the endo-tracheal tube for several days or weeks, it is common for the trachea to become irritated at the point where the cuff engages the tracheal wall, leading to necrosis, scarring, and possibly stenosis, (see Intratracheal Cuff: Performance Characteristics, By Carroll, Hedden and Safar, in Anesthesiology, September 1969, pages 275-281).
At least some of the causes of the difficulties with prior art cuffs can be traced to the fact that the pressure of the cuff, acting against the trachea, can be great enough to cut off the blood circulation in the trachea thus causing damage. The prior art has recognized that, in the period between inhalation and exhalation, the pressure in the cuff can be decreased to allow blood circulation to flow in the tracheal walls, (see, for instance, U.S. Pat. No. 3,481,339).
The prior art (see for example, U.S. Pat. No. 3,481,339) has also suggested that tubes with successive cuffs could be used, so that successive compression can be carried out with different parts or portions corresponding to each cuff. However, while the prior art teaches a cuff which is capable of automatically decompressing between inhalation and exhalation, U.S. Pat. No. 3,481,339 states that successive cuffs were disadvantageous since the assistance of an expert was required.